The present invention relates to a liquid crystal composition and a liquid crystal shutter arrangement containing such a composition, for example a liquid crystal display device including a multiplicity of liquid crystal shutters.
Liquid crystal devices having liquid crystal layers including ferroelectric liquid crystal compositions are the subject of active research interest. In the production of such devices, the liquid crystal layer is formed by introducing the liquid crystal composition at an elevated temperature so as to cause it to be in the isotropic (or nematic), free flowing phase into a narrow gap (the cell gap) between a pair of substrates. At this stage, the liquid crystal composition is at a temperature somewhat higher than its operating temperature. The liquid crystal composition is then cooled in a controlled manner until an optically active tilted smectic phase is achieved, typically the smectic C phase, SmC*, (the * denotes chirality or optical activity). In order for the liquid crystal composition to have the required advantageous properties, it is desired for it to pass from the isotropic phase (I) through chiral nematic (N*) and smectic A (SmA) phases before reaching the operative smectic C* phase. This is referred to as an I-N*-SmA-SmC* phase sequence. The temperature (TA-C) at which the transition from the SmA phase to the SmC* phase affects the working temperature range over which the device can operate. Thus, a low TA-C. effectively reduces the working temperature range of the device.
Liquid crystal compositions commonly comprise a host material such as those based on mixtures of two or more phenylpyrimidinyl compounds exhibiting or capable of exhibiting a smectic C phase, and optionally other materials which may be included to modify the properties of the host material, for example a chiral dopant to impart chirality if the host material is not inherently chiral, or to enhance or induce formation of certain phases in the phase sequence.
A liquid crystal composition has been proposed in which the host material is based on a 1:2 by weight mixture of the compounds [Ia] and [Ib]) below: 
Such a host material is formulated to have a low dielectric biaxiality and a low switching viscosity so that, in compositions containing a chiral dopant, a high value of Ps/xcex4xcex5 (spontaneous polarisation/dielectric biaxiality can be obtained. However, this material has a low TA-C, 54xc2x0 C., even before mixing with chiral dopant (which can suppress TA-C).
It is an object of the present Invention to provide a liquid crystal composition having an improved TA-C.